This relates generally to adhesives and, more particularly, to pressure sensitive adhesives.
Electronic devices often include components that are assembled using adhesives. Adhesives tend to be more compact than screws and other fasteners. Adhesives such as pressure sensitive adhesives, which are a class of adhesive that can be activated by application of pressure, are easier to rework than welds. The use of pressure sensitive adhesives may also help minimize assembly complexity and materials costs. Cellular telephones and other modern electronic devices often contain numerous joints formed from pressure sensitive adhesives.
Although pressure sensitive adhesives offer advantages over other techniques for forming joints in electronic devices, care must be taken to ensure uniform activation in a pressure sensitive adhesive layer. If pressure is unevenly applied during assembly, a pressure sensitive adhesive joint may have weak portions that are prone to failure.
To ensure that pressure sensitive adhesive joints are being formed properly, manufacturers can perform spot tests using special test units. In a typical scenario, parts in a test device are assembled using layers of pressure indicator film (sometimes referred to as pressure paper). The layers of pressure indicator film exhibit color changes that are proportional to applied pressure. If the layers of pressure indicator film indicate that pressure is being applied with inadequate uniformity, remedial changes can be made to the manufacturing process.
It is not always possible, however, to accurately predict how pressure sensitive adhesive joints will be formed from test results obtained using pressure indicator film. There is often a poor correlation between pressure indicator film tests and the actual pressure sensitive adhesive joints that are formed in production units, because pressure indicator film tests do not measure the actual pressures experienced by the adhesive.
It would therefore be desirable to provide improved ways for forming and evaluating pressure sensitive adhesive joints.